1. Field of the Invention
The present invention relates generally to a method and system for transmitting and receiving data in a mobile communication system. More particularly, the present invention relates to a method and apparatus for transmitting and receiving data to/from a plurality of users in a Code Division Multiple Access (CDMA) system using multiple carriers (MC).
2. Description of the Related Art
Recently, a great deal of research is being carried out on high-speed data transmission in CDMA mobile communication systems. A typical mobile communication system having a channel structure for high-speed data transmission includes a 1× EVolution Data Only (1×EVDO) system. The 1×EVDO system is a mobile communication system specified in the 3rd Generation Partnership Project 2 (3GPP2) for complementing data communication of an Interim Standard-2000 (IS-2000) system.
A forward channel of the 1×EVDO system includes a pilot channel, a forward Medium Access Control (MAC) channel, a forward traffic channel, and a forward control channel. The forward channel is transmitted to each access terminal (AT) by Time Division Multiplexing (TDM). A bundle of the TDM-transmitted signals is called a ‘burst.’
The forward traffic channel transmits user data packets, and the forward control channel transmits control messages and user data packets. The forward MAC channel is used for reverse rate control, delivery of power control information, and designation of a forward data transmission channel.
A reverse channel of the 1×EVDO system, unlike the forward channel, has a channel with a unique identification code for each individual access terminal, and the reverse channel for each individual access terminal includes a pilot channel, a reverse traffic channel, an access channel, a Data Rate Control (DRC) channel, and a Reverse Rate Indicator (RRI) channel. The reverse traffic channel transmits user data packets, the DRC channel is used for indicating a forward rate supportable by an access terminal, and the RRI channel is used for indicating reverse direction data channel transmission rate. The access channel is used when an access terminal transmits messages or traffic to an access node (AN) before the traffic channel is connected.
The architecture of a 1×EVDO system will now be described with reference to FIG. 1.
FIG. 1 is a diagram schematically illustrating architecture of a conventional 1×EVDO system.
Referring to FIG. 1, the 1×EVDO system includes a Packet Data Service Node (PDSN) 40, connected to the Internet network 50, for transmitting high-speed packet data to an access node 20, and an Access Node Controller (ANC) 30 for controlling the access node 20. The access node 20 wirelessly communicates with a plurality of access terminals (ATs) 10, and transmits the high-speed packet data to an access terminal 10a having the highest rate.
For rate control of the forward channel, the access terminal 10 measures the received strength of a pilot transmitted by the access node 20, and determines its desired forward data rate based on the measured received strength of the pilot. The access terminal 10 transmits DRC information corresponding to the determined forward data rate to the access node 20 through a DRC channel. The access node 20 then receives the DRC information, and can transmit packet data only to the access terminal 10a having a good channel state at the rate reported by the access terminal 10a. Although a mapping relationship between the forward channel state and the DRC information is subject to change depending on implementation, it is generally fixed in the access terminal manufacturing process.
Table 1 shows a relationship between a DRC reported by an access terminal and its associated rate and transmission format.
TABLE 1Num ofTransmissionDRCRate (kbps)Transmissions (slots)Format0x0016(1024, 16, 1024)0x138.416(1024, 16, 1024)0x276.88(1024, 8, 512)0x3153.64(1024, 4, 256)0x4307.22(1024, 2, 128)0x5307.24(2048, 4, 128)0x6614.41(1024, 1, 64)0x7614.42(2048, 2, 64)0x8921.62(3072, 2, 64)0x91228.81(2048, 1, 64)0xa1228.82(4096, 2, 64)0xb1843.21(3072, 1, 64)0xc2457.61(4096, 1, 64)0xd15362(5120, 2, 64)0xe30721(5120, 1, 64)
Referring to Table 1, the transmission format is expressed in the form of bit, slot, and chip preamble, for example, (1024, 16, 1024), which means that 1024-bit information is transmitted for 16 slots and a 1024-chip preamble is transmitted at the beginning of the transmission. An access node transmits data to each access terminal with a transmission format corresponding to a DRC value reported by the access terminal, and the access terminal attempts to receive a forward data channel only with the format corresponding to its reported DRC value. This agreement is made because for a data channel transmitted in the forward direction, there is no other channel to indicate its data rate. That is, when the access node transmits data using a transmission format other than the transmission format reported by the access terminal, there is no way to indicate the transmission format, so the access terminal cannot receive the data. Therefore, the access node always transmits data only with the transmission format corresponding to the DRC reported by the access terminal. For example, for the access terminal that transmitted DRC 0×01 through a DRC channel, the access node transmits data using a transmission format (1024, 16, 1024) corresponding to the DRC value, and the access terminal attempts to receive data only with this format.
The access node, when transmitting data to the access terminal, indicates which user should receive the forward data, using a preamble having the length specified in the transmission format. This preamble is generated by spreading a predefined bit sequence using a Walsh code corresponding to a Medium Access Control Identifier (MAC ID) assigned to each access terminal by the access node. In order to determine whether to receive the data, the access terminal receives as many chips as the preamble length corresponding to its reported transmission format, despreads the received chips using the Walsh code corresponding to its own MAC ID, and compares whether the signal is equal to the predefined bit sequence in terms of strength and value.
The packet data that the access node transmits to one access terminal according to the received DRC information is called a “Single User Packet (SUP).” For general data service, the access node transmits data using the SUP. The Voice over Internet Protocol (VoIP)-base data service, compared with the general data service, needs a lower transmission bandwidth of about 9.6 kbps. For a bandwidth of 9.6 kbps, data of only some 192 bits is transmitted every 20 ms. Transmitting such a small amount of data with the SUP having a minimum size of 1024 bits causes an unnecessary waste of the bandwidth. In order to prevent such a waste of resources in the wireless access section, a scheme of transmitting data for several users using one physical packet has been introduced Such a packet format is called a “Multi-User Packet (MUP).”
Table 2 shows a relationship between a DRC value and its associated rate and transmission format for the MUP.
TABLE 2RateList of AssociatedDRC(kbps)Multi-User Transmission Formats0x00(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256)0x138.4(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256)0x276.8(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256)0x3153.6(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256)0x4307.2(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256)0x5307.2(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128)0x6614.4(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256)0x7614.4(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128)0x8921.6(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128),(3072, 2, 64)0x91228.8(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128)0xa1228.8(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128),(3072, 2, 64), (4096, 2, 64)0xb1843.2(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128),(3072, 2, 64)0xc2457.6(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128),(3072, 2, 64), (4096, 2, 64)0xd1536(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128),(3072, 2, 64), (4096, 2, 64), (5120, 2, 64)0xe3072(128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128),(3072, 2, 64), (4096, 2, 64), (5120, 2, 64)
For each individual DRC reported by the access terminal, the 1×EVDO system defines a multi-user packet compatible with the DRC as shown in Table 2. For example, an access terminal that transmitted DRC 0×5 should receive a multi-user packet corresponding to a transmission format (128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128). This multi-user packet includes packet data for several users, and is transmitted together with an address of the access terminal that will receive each data packet. Upon receipt of the multi-user packet, the access terminal determines whether its own MAC ID is included in the received packet, and processes the corresponding user packet only when its own MAC ID is included in the received packet.
FIG. 2 is a diagram illustrating a structure of a multi-user packet used in a conventional 1×EVDO system. Referring to FIG. 2, a multi-user packet 200 is composed of a header 210 indicating a MAC ID, or an address, of a receiving access terminal and a length of data transmitted to the access terminal, a header delimiter 220 for defining a boundary between the header 210 and the other part, a payload 230 including data, a padding 240, and a trailer 250.
The header 210 of the multi-user packet delivers the information necessary for reception of the multi-user packet for each of the access terminals receiving the multi-user packet. This information is composed of a format field 211 containing format information of transmission data, a MAC ID 213, which is an identifier of a receiving access terminal, and a length field 215 indicating a length of the transmission data. Herein, the transmission data means transmission data in the multi-user packet 200, and will be referred to as a user packet.
The header 210, including N received information units for N receiving access terminals, is followed by the delimiter 220 of ‘00000000’ for defining a boundary between the header part and the payload part. The delimiter 220 is followed by the payload 230, including user packets for N access terminals according to data format and length, and the order designated in the previously transmitted/received information. The padding 240 can be attached to the rear of the payload 230 when necessary, and the trailer 250 fixed to ‘00’ is finally located at the rear of the padding 240, generating one multi-user packet 200.
The multi-user packet 200 is transmitted using a preamble assigned for transmission of a multi-user packet. Five preambles for the multi-user packet are defined according to rates of the multi-user packet. For example, one preamble (preamble #66) can be used for a low-rate multi-user packet (128, 4, 256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), one preamble (preamble #67) can be used for a multi-user packet (2048, 4, 128), and different preambles (preambles #68, 69 and 70) can be used for a multi-user packet (3072, 2, 64), (4096, 2, 64), (5120, 2, 64), respectively. An access terminal, after reporting the DRC, monitors whether a preamble corresponding to the multi-user packet compatible with the transmitted DRC has arrived. Upon receipt of the preamble corresponding to the multi-user packet compatible with its own DRC, the access terminal decodes the multi-user packet, determines whether its own address is included in the header part, and reads and processes the user packet corresponding to the length specified in the header from the payload part if its own address is included in the header part.
With increasing demand for higher data rates in mobile communication systems, a multi-carrier EVDO system has been proposed to obtain a higher rate in the 1×EVDO system. The multi-carrier EVDO system, compared with a conventional EVDO system that exchanges data using a single carrier, assigns a plurality of carriers to one access terminal, thereby implementing a higher rate. Because each carrier can provide the maximum rate provided by a conventional 1×EVDO system, an access terminal in communication using multiple carriers in the ideal environment can use the maximum data rate, which is a function of the number of carriers.
In such a multi-carrier system, because one access terminal receives more than one carrier, the number of access terminals receiving data for each individual carrier increases on average. Accordingly, there is a need for a method capable of providing as many MAC IDs as the increasing number of access terminals for each individual carrier. In addition, for simple switching, the multi-carrier system should not greatly modify the physical transmission structure of the existing 1×EVDO system from the preexisting nationwide network.